Who Created The Locked Up Doujin And Where To Buy It?

I dug into the whole situation around the 'Locked Up' doujin and here's the deal: it's almost certainly not an official part of any mainstream franchise. Most doujin works—even ones that riff hard on existing characters or settings—are fan creations produced by independent circles and self-published at events like Comiket or via platforms such as Booth, Melonbooks, or Pixiv. You'll usually see a circle name, a print-run note, and no publisher imprint like you'd expect from Kadokawa, Square Enix, or Shueisha. If you want hard signs, check the credits and the ISBN. Official tie-ins typically carry a publisher logo, an ISBN or official product code, and sometimes a clear licensing blurb. Doujin items tend to list a circle, an artist, maybe a warning about being fan-made, and limited release notes. I've picked up dozens of similar books at conventions and the absence of a publisher and the presence of event-only stamps is a giveaway. Also, art style similarity doesn't equal canonicity—creators often imitate a franchise for doujinshi without any licensing. So in short: unless 'Locked Up' was publicly announced as a licensed collaboration (which would show up on official franchise websites and shops), treat it as a fanwork. I still love how wildly creative some of those circles get, even when they're unofficial.